The present invention relates to a direct current motor drive circuit which drives a brushless direct current motor for rotating a magnet rotor by a motor coil which switches polarities of a plurality (for example, four) of magnetic poles when the direction of an applied current is changed.
FIG. 3 is a circuit diagram showing a conventional direct current motor drive circuit described in, for example, JP-A-9-331692.
In FIG. 3, the reference numeral 101 denotes a hall element which is disposed between magnetic poles formed by a motor coil (described later) forming a stator of a direct current motor and detects a rotating position of a magnet rotor, the reference numeral 102 denotes an IC which outputs a signal for switching the energization direction (direction of the applied current) of the motor coil, the reference numerals 105a and 105b denote P channel metal oxide semiconductor field effect transistors (referred to as MOSFETs), the reference numerals 106a and 106b are N channel MOSFETs, the reference numerals 130a through 132a and 130b through 132b denote transistors, the reference numeral 109 denotes a motor coil which switches polarities of a plurality (for example, four) of magnetic poles when the applied current direction is changed, and the reference symbol T denotes a power supply terminal to which a direct current power of a direct current voltage Vcc (for example, 12V) is supplied.
Herein, the transistors 131a, 131b, 132a, and 132b form a dead time generation circuit which generates a dead time for preventing power supply shortcircuits due to simultaneous energization when the phase is switched in the H-bridge circuit described later, the transistors 130a and 130b form an H-bridge drive circuit for driving the H-bridge circuit, and the P channel MOSFETs 105a and 105b, the N channel MOSFETs 106a and 106b, and the motor coil 109 form the H-bridge circuit. In FIG. 3, all circuits except for the motor coil 109 form a direct current motor drive circuit.
Connections and operations of the direct current motor drive circuit thus constructed are described.
An output of the IC 102 is connected to transistors 131a and 131b for low frequency amplifying, and outputs of the transistors 131a and 131b are connected to bases of PNP small signal transistors 130a and 130b which drive gates of the MOSFETs, respectively, outputs of the transistors 131a and 131b are connected to bases of the transistors 132b and 132a, respectively, collectors thereof are connected to the transistors 130b and 130a, emitters of the small signal transistors 130a and 130b are connected to gates of the P channel MOSFETs 105a and 105b and collectors of the small signal transistors 130a and 130b are connected to gates of the N channel MOSFETs 106a and 106b, and the transistors 130a and 130b are alternately turned on and off by the IC 102 that outputs a signal for switching the energization direction of the motor coil 109.
When the transistor 130a is on, the MOSFETs 105a and 106a are turned on, the motor coil 109 is energized from left to right, and thereafter, when the transistor 130a is turned off, the transistor 130b is turned on and the MOSFETs 105b and 106b are turned on and a current in reverse to the previous direction is supplied to the motor coil 109.
Thus, in a conventional direct current motor drive circuit, the transistors 131a, 131b, 132a, and 132b form a dead time generation circuit and the transistors 130a and 130b form an H-bridge drive circuit. Therefore, in a brushless DC motor or the like adapted to alternating current inputs by converting an alternating current voltage inputted from a power supply terminal into a direct current voltage by a rectifier circuit (not shown) in the motor, when the direct current voltage Vcc is high, for example, 110V (namely, when the H-bridge circuit is made so as to withstand a higher voltage), the transistors 130a through 132a and 130b through 132b must also be changed to high-withstand voltage transistors, and the direct current motor drive circuit becomes expensive.
In this direct current motor drive circuit, it has been demanded that the direct current motor drive circuit can be simplified and prevented from becoming expensive even when the H-bridge circuit is made so as to withstand a higher voltage.